The present invention relates to apparatus used in the semiconductor manufacturing art for heating an effusion cell having an evolving ingredient in a molecular beam epitaxy furnace. Specifically, a replaceable heating assembly for the effusion cell having a vacuum separate from the main furnace vacuum is provided.
Molecular beam epitaxy techniques have been described which permit growing epitaxial layers of semiconductor crystals. In vacuum epitaxy techniques, thin films of crystalline material are deposited on a substrate by evaporating material in a vacuum system onto the surface of a substrate. Vacuum epitaxy processes are carried out in a high vacuum which contains a heated substrate. Effusion ovens are provided for heating the materials to be deposited. The material effuses atoms of the semiconductor constituent through an orifice in the effusion cell oven. A controlled flux of effused semiconductor constituent material may be generated which is controlled by oven temperature and the size of the oven orifice.
In order to obtain high crystalline and semiconductor quality of the epitaxial layers, the vacuum environment of the substrate must be maintained free of contaminants. In the past, the heating element of the effusion oven has been a source of contaminants. Typically, a heating element consists of a wire or mesh surrounding a crucible containing the source material. Insulators may be present to separate the current carrying elements. Reactions between the insulator and refractory metals of the effusion ovens can result, providing another source of contaminants. Experience has shown that 1 part in 10.sup.7 or less contamination of the semiconductor atoms will result in observable effects to the resulting crystal structure.